1. Field of the Invention
The invention relates to the field of microstructure manufacturing as well as the treatment of substrates in semiconductor materials.
2. Background of the Related Art
In microelectronics, certain operations, such as bonding operations, require that the surfaces to be bonded are as smooth as possible. However, the manufacturing of certain devices, particularly devices implementing a membrane or mobile part, may necessitate having recourse to surfaces that face each other but that do not adhere to each other, to justly prevent ill-timed bondings of the membrane on the facing surface and to maintain mobility of the membrane.
French Patent No. FR 2857953 discloses a process for manufacturing Bonded Silicon on Insulator (BSOI) type structures in which a structured zone is made, thus preventing bonding to another surface. This type of structure finds application in the field of Micro-Electro-Mechanical Systems (MEMS) generally, and more particularly in the case where a superficial silicon membrane must be released to manufacture sensors.
During the membrane release step, which may include an underlying oxide attack, the membrane may bond to the substrate, which may cause the sensor to malfunction. This bonding may also happen during operation of the sensor.
As explained in the document cited above, a BSOI substrate that comprises a rough buried interface avoids this problem since the roughness of the buried interface prevents any bonding between the membrane and the support.
French Patent No. FR 2857953 discloses roughening of a surface using various techniques, such as mechanical and/or chemical thinning (mechanical-chemical polishing, grinding, TMAH or HF/HNO3 etching). These techniques may create defects on the surface of the semiconductor substrate (and even in the depth of the substrate in the case of grinding) that may generate defects on the specific BSOI antisticking substrate during manufacturing (for example bonding defects or structural defects in the SOI layer). In the case where the roughened substrate is thinned to become the active layer, these defects may interfere with the fabrication of certain types of components.
Roughening may also be accomplished by deposition of a non-monocrystalline material, which is different from the monocrystalline substrate. As a result of this process, the material deposited has physical properties that are different from those of the starting substrate, such as thermal and/or electrical conductivity properties. This difference in physical properties may interfere with certain applications.
Consequently, a process is needed that allows a rough surface to be made on a substrate without increasing the density of defects on the initial substrate and without modifying its main physical characteristics.